Lube basestocks are commonly used for the production of lubricants, such as lubricating oils for automobiles, industrial lubricants and lubricating greases. They are also used as process oils, white oils, metal working oils and heat transfer fluids. Finished lubricants consist of two general components, lubricating base oil and additives. Lubricating base oil is the major constituent in these finished lubricants and contributes significantly to the properties of the finished lubricant. In general, a few lubricating base oils are used to manufacture a wide variety of finished lubricants by varying the mixtures of individual lubricating base oils and individual additives.
According to the American Petroleum Institute (API) classifications, lube basestocks are categorized in five groups based on their saturated hydrocarbon content, sulfur level, and viscosity index (Table 1). Lube base oils are typically produced in large scale from non-renewable petroleum sources. Group I, II, and III basestocks are all derived from crude oil via extensive processing, such as solvent extraction, solvent or catalytic dewaxing, and hydroisomerization. Group III base oils can also be produced from synthetic hydrocarbon liquids obtained from natural gas, coal or other fossil resources. Group IV basestocks, the poly(alpha olefins) (PAO), are produced by oligomerization of alpha olefins, such as 1-decene. Group V base oils includes everything that does not belong to Groups I-IV, such as naphthenics, polyalkylene glycols (PAG), and esters.
TABLE 1API classificationGroup IGroup IIGroup IIIGroup IVGroup V% Saturates<90≧90≧90PolyAll others% S>0.03≦0.03≦0.03alpha-not belong-Viscosity80-12080-120≧120olefinsing to groupIndex (VI)(PAO)I-IV
Increasingly, the specifications for finished automotive lubricants require products with excellent low temperature properties, high oxidation stability and low volatility. Generally lubricating base oils are base oils having kinematic viscosity of 3 cSt or greater at 100° C. (Kv100); pour point (PP) of −12° C. or less; and viscosity index (VI) 90 or greater. In general, high performance lubricating base oils should have a Noack volatility no greater than current conventional Group I or Group II light neutral oils. Currently, only a small fraction of the base oils manufactured today are able to meet these demanding specifications.
For environmental, economical, and regulatory reasons, it is of interest to produce fuels, chemicals, and lube oils from renewable sources of biological origin. So far only esters of renewable and biological origin have been used in applications such as refrigeration compressor lubricants, bio-hydraulic oils and metal working oils. In automotive and industrial lubricants, esters from biological sources are used in very small fractions as additives due to technical problems as well as their high prices. For example, ester base oils can hydrolyze readily producing acids, which in turn cause corrosion on lubricating systems.
In contrast, lube basestocks consisting of hydrocarbons from biological sources do not have those technical problems associated with esters from same sources. Most common biological sources for hydrocarbons are natural oils, which can be derived from plant sources such as canola oil, castor oil, sunflower seed oil, rapeseed oil, peanut oil, soy bean oil, and tall oil, or derived from animal fats. The basic structural unit of natural oils and fats is a triglyceride, which is an ester of glycerol with three fatty acid molecules having the structure below:
wherein R1, R2, and R3 represent C4-C30 hydrocarbon chains. Fatty acids are carboxylic acids containing long linear hydrocarbon chains. Lengths of the hydrocarbon chains most commonly are 18 carbons (C18). C18 fatty acids are typically bonded to the middle hydroxyl group of glycerol. Typical carbon numbers of the fatty acids linked to the two other hydroxyl groups are even numbers, being between C14 and C22.
For the purpose of this disclosure, when all the fatty acid chains in a triglyceride have more than 14 carbon atoms, the triglyceride is considered a long-chain fatty acid triglyceride. When one or more of the fatty acid chains in a triglyceride has less than 14 carbon atoms, the triglycerides are considered medium-chain triglycerides.
Fatty acid composition of feedstocks of biological origin may vary considerably depending on the source. While several double bonds may be present in fatty acids, they are non-conjugated (with at least one —CH2— unit between the double bonds). With respect to configuration, the double bonds of natural fatty acids are mostly of cis form. As the number of the double bonds increase, they are generally located at the free end of the chain. Lengths of hydrocarbon chains and numbers of double bonds depend on the various plant or animal fats or waxes serving as the source of the fatty acid. Animal fats typically contain more saturated fatty acids than unsaturated fatty acids. Fatty acids of fish oil contain high amounts of double bonds, and the average length of the hydrocarbon chains is higher compared to fatty acids of plant oils and animal fats.
Fatty acid triglycerides can also be illustrated by way of example by the following structure:
From bottom to top, the fatty acid chains are palmitic, oleic, and linoleic acid. Depending on the source, each of the fatty acid chains can contain between 14 and 22 carbons. Table 2 below provides the fatty acid composition of some common oils from plant and animal sources.
TABLE 2Mono-Poly-Saturated (%)Unsaturated (%)Unsaturated (%)Animal fatsLard40.843.89.6Butter54.019.82.6Vegetable oilsCoconut oil85.26.61.7Palm oil45.341.68.3Cottonseed25.521.348.1oilWheat germ18.815.960.7oilSoya oil14.523.256.5Olive oil14.069.711.2Corn oil12.724.757.8Sunflower11.920.263.0oilSafflower oil10.212.672.1Rapeseed/5.364.324.8Canola oil
Metathesis of triglycerides and ethylene is disclosed in U.S. Pat. No. 4,545,941, which is incorporated herein by reference. Alpha-olefins and modified triglycerides are produced. Alpha olefins obtained by the disclosed process can be used in the synthesis of lubricating oils, detergents, plasticizer alcohols, flavors, perfumes, dyes, pharmaceuticals, and resins. Medium-chain triglycerides can be used as dietary components or be converted via hydrolysis to medium-chain fatty acids suitable for a variety of industrial purposes, such as ingredients for soap and “hard butter”. Transformation of medium chain triglycerides via hydroisomerization to lubricants is not disclosed in the prior art.
Branched alkyl fatty acids and esters are useful in a number of consumer products including lubricants. Branched fatty acids and alkyl esters that are saturated offer a number of useful features, including better lubricity due to their chain length and random branching, better oxidative stability due to low or no double-bond content, and lower pour point compared to their linear counter-parts. U.S. Pat. No. 6,455,716 discloses a process for the branching of saturated and unsaturated fatty acids and/or alkyl esters thereof by skeletal isomerization over acid/metal bi-functional catalysts.
Currently, group IV lube basestocks (PAO) are manufactured by oligomerizing alpha-olefins from petroleum sources, such as disclosed in U.S. Pat. No. 5,451,704.
With increasing availability of triglycerides it is desirable to take advantage of the renewable feedstocks to produce lube basestocks, thus saving non-renewable petroleum raw materials. There is a need for an integrated process to make both group IV and group V lube basestocks from renewable sources, especially from triglycerides of long-chain fatty acids.